The term 'plural possessive' refers to a grammatical construction in which a noun or pronoun is modified to indicate possession by more than one person or thing. The three crossword solutions for this term are OURS (4 letters), THEIR (5 letters), and OUR (3 letters). OURS is the plural possessive form of the pronoun 'our, ' indicating possession by more than one person. THEIR is the plural possessive form of the pronoun 'they, ' indicating possession by more than one person or thing. Finally, OUR is the singular possessive form of the pronoun 'our, ' indicating possession by one person.